Laser System for Atom Interferometry

Andrew Chew

Content

• Overview of related Theory

• Experimental Setup:– Raman Laser System– Frequency/Phase Stabilization

• Outlook

Atom Interferometry

• Similar to Light Interferometry

• Atoms replace role of the light. • Atom-optical elements replace mirrors and beam splitters

Motivation

• Light Interferometry is used to make inertial sensors but the long wavelength limits the resolution of the phase measurement.

• The atomic de Broglie wavelength is much shorter and thus allows for greater resolution of the phase measurement.

• Atoms have mass and thus we can make measurements of the forces exerted on them.

• An example would be the measurement of the gravitation force.

Raman Transitions

• Stimulated Raman Transitions result in the super position of |e› and |g› states

• Two phase-locked Lasers of frequency ω1 and ω2 are used to couple the |g,p› and |i,p+ ħk1› states, and the |e, p + ħ(k1-k2)› and |i› states respectively.

• A large detuning Δ suppresses spontaneous emission from the intermediate |i,p+ ħk1› state.

• The ground states are effectively stable.

Ramsey-Bordé Interferometer

• A sequence of π/2, π and π/2 Raman pulses

• 1st π/2 pulse acts a beam splitter: Places the atomic wave in a superposition of |g,p› and |e, p + ħkeff› states

• π pulse acts a mirror: Flips the |g,p› to the |e, p + ħkeff› states and vice versa

• 2nd π/2 pulse acts a beam splitter: Projecting the atoms onto the initial state.

Laser System

• Extended Cavity Diode Laser (ECDL) design used by Gilowski et. al in Narrow bandwidth interference filter-stabilized diode laser systems for the manipulation of neutral atoms. Optics Communications, 280:443-447, 2007.

• 3 Master Oscillator Power Amplifier (MOPA) systems for each wavelength, each consisting of an ECDL as the seeder and a Tapered Amplifier as the amplifier. One MOPA is for cooling, another two for Raman lasers.

• Repumper laser consisting of one DFB laser diode.

Experimental Setup

• Laser system for Rubidium consisting of cooling and repumper lasers for preparation of atomic cloud.

• Raman laser system for atom interferometry.

• Laser system for imaging and detection of internal atomic states.

• 1 set of laser systems for each individual species of atoms used for interferometry

Raman Lasers

Raman Lasers

• The Raman lasers must be stabilized to stable frequency references to ensure that the frequency separation between them is kept at 6.84GHz.

• The Raman lasers are overlapped to produce the laser beat note.• The laser beat note is amplified and mixed with a 7GHz reference

oscillator then filtered with a low-pass filter to produce a 160MHz signal.

Raman Lasers

• The beat note is then passed into a PLL board where the frequency divided by 2 and then is compared against a 80MHz frequency reference using a digital phase-frequency detector.

• The signal is then filtered, integrated and two outputs are produced: one fast and one slow for the laser current and the laser piezo feedback.

Vacuum System

• Vacuum Chamber consists of 2 glass cells and a central metallic vacuum chamber.

• A Titanium Ion-Getter Pump and A Titanium Sublimation pump is attached to the Vacuum chamber

• The Ion Getter pump operates continuously, while the Titanium Sublimation pump is operated initially during baking and then switched off.

• There are dispensers to introduce the Rubidium and Cesium atoms into the vacuum system.

• Prior to use, the vacuum system is baked with a rotary vane pump and a turbomolecular pump running together with other two pumps.

• A Mass Spectrometer is used to monitor the gas pressure levels.

• We need a vacuum pressure of 10-10 mbar.

Outlook

• Near term we plan to complete the PLL for the Raman Lasers

• Next step is the Characterize the PLL

• And then work on other aspects such as getting the detection beam ready etc.

• Then We can do interferometry of Rubidium